1. Field of the Invention
This relates to a method for producing a print-out image which is resistant to background print-up comprising imagewise exposure of a certain internally sensitive photographic silver halide material containing an electron-accepting agent, to illumination having an intensity greater than about 3 watts per square centimeter. One aspect of the invention is a method for producing a print-out image as described in which the photographic material, after imagewise exposure, may be surface developed by means of a surface developer or internally developed by means of an internal developer.
2. Description of the State of the Art
It is well known that photographic silver halide materials for image recording are of two types: developing-out and print-out. The developing-out type of photographic silver halide requires that the imagewise exposed photographic silver halide material be chemically or physically developed, and then fixed and washed to provide a stable, visible image. The print-out type photographic silver halide requires no chemical processing and may or may not be stabilized and fixed. These print-out materials generally have a much slower photographic speed than developing-out photographic materials. Moreover, the images from a print-out photographic silver halide material have encountered a problem following imagewise exposure. This problem involves the instability of the background areas of the resulting image. After print-out the instability results in obliteration of the image by background density increases as a function of time, ambient illumination and other conditions. It has been desirable to provide a process for providing print-out images in a photograhic silver halide material which produces increased resistance to background print-up following imagewise exposure.
Print-out direct positive images have been obtained by exposure of a silver bromide photographic emulsion which contained an electron-accepting compound and have been uniformly fogged to a visible density. Such materials are described in, for example, U.S. Pat. No. 3,650,758 of Gilman, issued Mar. 21, 1972. While such print-out silver halide materials, which are also known as bleach-out materials, are useful for providing a direct positive print-out image in some uses, these materials have not provided the degree of stability that is desired in many uses.
Photosensitive silver halide emulsions that contain internally fogged photosensitive silver halide also are well known. For example, a photosensitive emulsion containing internally fogged photosensitive silver halide grains having substantially no surface fog on the grains can be prepared, such as described in U.S. Pat. No. 3,271,157, by mixing a silver salt solution with a halide solution in a liquid reaction medium wherein the silver salt solution contains a certain percent of iodide per mole of silver and a certain amount of a thioether silver halide solvent. The resulting emulsion can be useful for forming direct positive or negative images. The emulsions are especially useful because they enable use of surprisingly high concentrations of sensitizing dye on the silver halide grains. However, no indication is given that the emulsions can be useful for forming print-out images that have high resistance to background degradation following imagewise exposure.
There has accordingly been a continuing need to provide a method for producing improved print-out images with photographic silver halide materials which are resistant to background print-up.